Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913 the Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation. Silver halide radiographic elements account for the overwhelming majority of medical diagnostic images.
In recent years a number of alternative approaches to medical diagnostic imaging, particularly image acquisition, have become prominent. Medical diagnostic devices such as storage phosphor screens, CAT scanners, magnetic resonance imagers (MRI), and ultrasound imagers allow information to be obtained and stored in digital form. Although digitally stored images can be viewed and manipulated on a cathode ray tube (CRT) monitor, a hard copy of the image is almost always needed.
The most common approach for creating a hard copy of a digitally stored image is to expoe a radiation-sensitive silver halide film through a series of laterally offset exposures using a laser, a light emitting diode (LED) or a light bar (a linear series of independently addressable LED's). The image is recreated as a series of laterally offset pixels. Initially the radiation-sensitive silver halide films were essentially the same films used for radiographic imaging, except that finer silver halide grains were substituted to minimize noise (granularity). The advantages of using modified radiographic films to provide a hard copy of the digitally stored image are that medical imaging centers are already equipped to process radiographic films and are familiar with their image characteristics.
A typical film, KODAK EKTASCAN HN.TM., for creating a hard copy of a digitally stored medical diagnostic image includes an emulsion layer coated on a clear or blue tinted polyester film support. The emulsion layer contains a red-sensitized silver iodobromide (2.5 mol % iodide ion, based on total silver) cubic grain (0.33 .mu.m ECD) emulsion coated at a silver coverage of 30 mg/dm.sup.2. A conventional gelatin overcoat is coated over the emulsion layer. On the back side of the support a pelloid layer containing a red-absorbing antihalation dye is coated. A gelatin interlayer, used as a hardener incorporation site, overlies the pelloid layer, and a gelatin overcoat containing an antistat overlies the interlayer. Silver halide is relied upon to provide the infrared density required to activate processor sensors. No dye is introduced for the purpose of increasing infrared absorption.
It is the prevailing practice to process black and white radiographic films, including the film described above, in 90 seconds or less in an automatic process. For example, the Kodak X-OMAT 480 RA.TM. rapid access processor employs the following conventional processing cycle:
______________________________________ Development 24 seconds at 35.degree. C. Fixing 20 seconds at 35.degree. C. Washing 20 seconds at 35.degree. C. Drying 20 seconds at 65.degree. C. ______________________________________
with up to 6 seconds being taken up in film transport between processing steps.
A typical developer has the following composition:
______________________________________ Hydroquinone 30 g PHENIDONE 1.5 g KOH 21 g NaHCO.sub.3 7.5 g K.sub.2 SO.sub.3 44.2 g Na.sub.2 S.sub.2 O.sub.3 12.6 g NaBr 35.0 g 5-Methylbenzotriazole 0.06 g Glutaraldehyde 4.9 g Water to 1 liter/pH 10.0 ______________________________________
A typical fixing solution has the following composition:
______________________________________ Ammonium thiosulfate, 58% 260.0 g Sodium bisulfite 180.0 g Boric acid 25.0 g Acetic acid 10.0 g Water to 1 liter/pH 3.9-4.5 ______________________________________
Following development and fixing, the process typically includes a washing step whereby processing chemicals are washed out of the radiographic film using water, and a drying step. The film processed in this manner is then ready for image viewing.
Radiographic film processors such as the RA 480 processor are capable of processing large amounts of film over extended periods of time (e.g., a month or more) before its processing solutions are drained and replaced. Extended use of the processing solutions is made possible by the addition of small amounts of developer and fixer replenishers as each film is processed to compensate for developer and fixer losses by evaporation and film pick up.
Current technology utilizes developer and fixing solution replenisher solutions comprising similar components and concentrations as the original developer and fixing solutions. A suitable replenishment rate allows for stable sensitometry as numerous films are processed. Without any replenishment, sensitometry eventually would become unsatisfactory (that is, loss in film speed). Yet, there is a desire in the industry to reduce replenishment rates as much as possible so the costs of processing radiographic films can be reduced, and less effluent is discharged to the environment, thereby contributing to lower health care costs and environmental concerns. This must be done, however, without sacrificing sensitometric results as important health decisions are obviously based on having accurate images in radiographic films.
Generally the replenishment rate for the radiographic film developer is about 60 ml per 238 in.sup.2 (14.times.17 inch sheet) or per 0.154 m.sup.2 (35.6.times.43.2 cm sheet), and the fixing solution replenishment rate is about 80 ml for the same area. With increasing pressure to reduce effluent to the environment even more, it would be desirable to reduce these rates further if possible.
Thiaalkylene bisquaternary ammonium salts have been employed for a variety of purposes in silver halide photography. They are thioethers and hence capable of acting as grain ripening agents. They have been used also in fixing solutions, and as fog reducing agents. In copending and commonly assigned U.S. Ser. No. 08/574,508, filed Dec. 19, 1995 by Dickerson et al, these salts (known as "Quadt salts") are described as being incorporated into silver bromochloride radiographic films to increase imaging speed. They can also be included in the developer or activator solutions used for processing such films. When employed in the films, the Quadt salts tend to leach out into the developer and developer pH drops because of by-products from development.
There is a need in the art for a processing method for radiographic films containing Quadt salts that uses inexpensive and effective low developer replenishment rates while maintaining desired sensitometric properties, such as photographic speed. It would also be desired to extend the life of the developer solution so that less effluent is discharged to the environment.